<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
       .jjb{
        width: 100px;
        height: 100px;
        background-color: red;
       }

    </style>
</head>
<body>
    <div class="jjb">这是div标签</div>
</body>
</html>